1. Field of the Invention
The present invention relates generally to a safety device, and more particularly to a safety device that completely stops a driving system of an electric machine such as a printer or an industrial machine.
2. Description of Related Art
Japanese Patent Provisional Publication No. 5-345458 discloses a safety device for a laser printer. Since a laser of the laser printer emits a laser beam that is harmful to human eyes, the safety device cuts off the power supply to the laser to guarantee the user""s safety when the user opens a door of the printer.
The safety device has two switches that open and close according to whether the door of the printer is open or closed. When the user opens the door, the switches open or close to stop the operation of the printer. When the user opens the door, the safety device temporarily stores a signal indicating whether one of the switches is open or closed and keeps a signal indicating whether the other switch is open or closed for a predetermined time to completely stop the laser.
However, the safety device needs a complicated circuit that processes the signals from the switches. Thus, the circuit is unreliable and expensive.
In view of the foregoing, it is an object of the present invention to provide a reliable safety device that can completely stop a driving system with a simple and inexpensive circuit.
To achieve the above-mentioned object, the present invention is directed to a safety device comprising: a first determining device and a second determining device which separately determine whether or not an object is in a state that causes danger; a power supplying/cutting device which supplies power to a buffer when the first determining device determines that the object is not in the state that causes danger, and which cuts off the power supply to the buffer when the first determining device determines that the object is in the state that causes danger; a controlling device which outputs a controlling signal for operating a driving system to the buffer when the second determining device determines that the object is not in the state that causes danger, and which outputs a controlling signal for stopping the driving system to the buffer when the second determining device determines that the object is in the state that causes danger; and the buffer which outputs a driver controlling signal to the driving system to operate the driving system when the power supplying/cutting device supplies the power to the buffer and the controlling device outputs the controlling signal for operating the driving system to the buffer, and which does not output the driver controlling signal to the driving system to stop the driving system when the power supplying/cutting device cuts off the power supply to the buffer and the controlling device outputs the controlling signal for stopping the driving system to the buffer.
According to the present invention, the first determining device and the second determining device separately determine whether or not the object provided in the apparatus to which the safety device is applied is in the state that causes danger. The object may be a door, a moving part, etc. provided in the apparatus to which the safety device is applied. When the object is not in the state that causes danger, the power supplying/cutting device supplies the power to the buffer, and the controlling device outputs the controlling signal for operating the driving system to the buffer. Then, the buffer outputs the driver controlling signal to the driving system to operate the driving system. The driving system may be any electric device such as a power driver (e.g., an electric motor), a laser, a light emitting device and a heater, or a driving circuit for any of them.
When the object is in the state that causes danger, the power supplying/cutting device cuts off the power supply to the buffer, and the controlling device outputs the controlling signal for stopping the driving system to the buffer. The buffer does not output the driver controlling signal to the driving system to stop the driving system.
The safety device stops the driving system with the software when the second determining device determines that the object is in the state that causes danger and stops the driving system with the hardware when the first determining device determines that the object is in the state that causes danger. Therefore, the safety device can completely stop the driving system.
The first determining device and the second determining device may be switches that open and close according to whether or not the object is in the state that causes danger, or sensors that convert the information indicating the state of the object into an electric signal.
The power supplying/cutting device may be a transistor that turns ON and OFF according to whether or not the first determining device determines that the object is in the state that causes danger. Thus, the processing circuit for processing the information from the two determining devices can be simplified as one transistor and one buffer IC.
The buffer may comprise a plurality of input/output parts; and hence, the safety device can simultaneously stop a plurality of driving systems when at least one of the first and second determining devices determines that the object is in the state that causes danger.
The determining devices may determine whether a door of a printer is open or closed so that the safety device stops the driving system of the printer when the door is open. The determining devices may determine whether a paper tray of a printer is loaded in the printer or drawn from the printer so that the safety device stops the driving system of the printer when the paper tray is drawn from the printer.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.